There is known a mask generator that generates a mask having a plurality of data bits with a first logic level and a plurality of data bits with a second logic level (refer to Patent Document 1). A decoder decodes a first binary address indicating a start data bit position for data masking and a second binary address indicating an end data bit position for data masking. In response to an output of the decoder, a first lookahead carry unit generates a first carry bit that is to be propagated from a low-order bit position to a high-order bit position in a mask. In response to the output of the decoder, a second lookahead carry unit generates a second carry bit that is to be propagated from a high-order bit position to a low-order bit position in the mask.
There is also known a masking circuit that includes a first mask generating circuit and a second mask generating circuit and supplies elements of mask data that the second mask generating circuit outputs, as auxiliary inputs to a plurality of unit mask generating circuits of the first mask generating circuit (refer to Patent Document 2). In the first mask generating circuit, the plural unit mask generating circuits are arranged in parallel, the plural unit mask generating circuits each receiving n-bit binary data and the auxiliary input outputted from the second mask generating circuit and generating and outputting mask data in which a logical product as an element is included and a carry output. The second mask generating circuit receives the plural carry outputs outputted from the respective plural unit mask generating circuits of the first mask generating circuit and logic value “1” or an auxiliary input supplied from a similar masking circuit on a post-stage and generates and outputs mask data in which logical products as elements are included and a carry output.    [Patent Document 1] Japanese Laid-open Patent Publication No. 02-12327    [Patent Document 2] Japanese Laid-open Patent Publication No. 60-258642
A processing circuit is required to perform various kinds of processing, and an increase in its processing speed is required.